PURPOSE: To improve the manufacturing efficiency of hollow FRP members eliminating the removing work of core members and to obtain lightweight products, by making core members with foamed resin and fusing the core members with the heat in secondary heat treatment.

CONSTITUTION: A core member 11 is made with foamed resin such as foamed propylene or the like and formed into rectangular rod, and fiber bundles impregnated with matrix resin are wound around the core member 11. Then the outer periphery of the fiber bundles is covered with a forming frame, and the matrix resin is hardened by means of a primary heat treatment. Then the frame is removed to heat the matrix resin in a secondary heat treatment. By the secondary heat treatment, the core member 11 made of foamed propylene or the like is fused and shrunk, and tap shrunk residue is adhered firmly to the inner periphery to form a hollow inside.